(a) Field of the Invention
The present invention relates to vertically aligned (VA) liquid crystal alignment layer of a liquid crystal display. In particular, the present invention relates to the composition of a liquid crystal alignment layer of a liquid crystal display that is capable of improving the ODF (one drop filling) blemish defect of a liquid crystal display, by reducing drop blemishes and improving the dropping process margin.
(b) Description of the Background
As fifth and seventh generation LCDs emerge, liquid crystal displays (LCD) are becoming larger in size, for example, 1870×2200 mm). The ODF process is an essential liquid crystal dropping process, in terms of processing time and line capability in manufacturing such large LCDs.
In the liquid crystal dropping process, a liquid crystal dispenser or a stage is moved while dotting a specific amount of liquid crystal onto a substrate in a specific pattern as shown in FIG. 3. The cell gap of the liquid crystal is determined by the column spacer and its accuracy is affected by the amount of the liquid crystal that is being deposited.
Although the ODF process has many advantages over the conventional vacuum filling process in which liquid crystal material is injected between two substrates, new types of defects emerge from the ODF process. A typical example of such defects is the drop blemish.
A drop blemish results from the difference in retardation at the area where the liquid crystal has been dropped during the ODF process and the area where the liquid crystal has not been dropped. While this difference has not been fully understood, one plausible theory that is supported by experimentation argues that when two substrates are adjoined, the liquid crystal dropped on the alignment layer exerts flow (shear) force to the alignment layer and damages it. As a result, the pretilt angle of the alignment layer, etc. are changed and a blemish is formed.
A change in the pretilt angle of the alignment layer may disappear during heat treatment after the ODF process. However, if the deformation is severe, the change in pretilt angle may persist and form a drop blemish.
Conventional alignment layers have been developed with regard to the voltage holding ratio (VHR) and the residual DC (RDC), without an external force being applied, without considering drop blemishes. The surface energy of the alignment layer is set lower than the modal alignment layer of the display, and thus the liquid crystal becomes less spreadable.